Process for converting hydrocarbons



NOV. 25, 1947. WI Q. KEELING PROCESS FOR CONVERTING HYDROCARBONSOriginal Filed Deo. 19, 1940 Patented Nov. 25, 1947 PROCESS FORCONVERTING HYDRO- CARBONS William O. Keeling, Mount Lebanon, Pa.

Continuation of application Serial No. 370,827, December 19, 1940. Thisapplication January 11, 1945, Serial No. 572,380

14 Claims. 1

This invention relates to a process for converting hydrocarbons of lessvaluable properties into products having more valuable properties, andmore particularly to the combination of vapor-phase cracking,polymerization, and dehydrogenation in such a manner as to result in asingle, unitary process by means of which increased yields of motorfuel, having high octane ratings, are obtained in a novel and economicalmanner. This application is a continuation of my application Serial No.370,827, led December 19,

1940, for Process of converting hydrocarbons.

This application is a continuation-in-part of my co-pending application,Serial Number 101,765, led September 21, 1936, and Patent No.

2,363,532, issued November 28, 1944, which disclosed a cracking processin which conversion occurs, in the vapor-phase, in two stages. In theprimary conversion stage, the necessary heat was supplied to the vaporsbeing converted by indirect heat exchange; as for example, in apipe-still coil; and in the secondary stage by direct admixture of thevapors with a suitable heat carrier gas.

Dhydrogenation of saturated hydrocarbons by means of heat or thecombination of heat and catalysts has long been known in the art. Whenheat alone is used, it is difficult to carry the dehydrogenation to asatisfactory degree of completion without causing other and undesirablereactions. But when catalysts are used in conjunction with heat,dehydrogenation may be carried out almost quantitatively and, bysuitable regulation of temperature and space velocities, Without causinga substantial amount of undesirable reactions. Dehydrogenation by meansof heat alone is ordinarily carried out at temperatures ranging fromapproximately 1100- 1800 F. But with catalysts, it may be carried out attemperatures ranging from approximately 600-1500 F., depending upon thecatalyst used. For the purpose i this invention, either method ofdehydrogena on may be used. Where a limited amount of hydrocarbonssuitable for a heat carrier gas is available, and where a very high heatcarrier gas temperature is desired, dehydrogenation by means of heatalone may be practiced. Where moderate heat carrier gas temperatures aswell as a maximum volume of the resulting unsaturated gases are desired,dehydrogcnation by means of a suitable catalyst may be practiced.

Similarly, polymerization of unsaturated hydrocarbons can beaccomplished by the application of heat and pressure. But polymerizationmay -be speeded up and larger yields of polymers obtained by the use ofcatalysts, the temperatures and pressures used varying with the natureof the catalyst. In this process some polymerization of the unsaturatesin the heat carrier gas may occur in the cracking stage, but the majorportion will preferably occur in the subsequent polymerization zone,where conditions of temperature and pressure are maintained which areprimarily suited to promote polymerization by the particular catalystemployed. These temperatures and pressures may vary from 300 to 1100 F.,and from atmospheric up to several thousand pounds per square inch,depending on the catalyst.

Numerous processes for cracking hydrocarbons have been proposed, but theone preferred is that disclosed in my copendlng applications, SerialNumbers 101,765 and 597,692. In this process the charging stock isvaporized, the evolved vapors separated from any unvaporized residue;the vapors are then further heated by indirect heat exchange as in apipe-still coil, and cracking is completed by directly admixing theheated vapors with a suitable heat carrier gas of suilcient volume andtemperature to supply the necessary amount of heat to complete theconversion.

I have found that the steps of vapor-phase cracking, dehydrogenation,and polymerization, with certain modications to be described, can

be combined into a single, unitary process forl converting hydrocarbonsinto motor fuels of high octane rating, with greater yields and at lesscost than if these three steps were separately practiced on the samecharging stocks.

As preferably practiced in this invention, the combination of thesethree steps is substantially as follows: Hydrocarbons, preferably thosecontaining from 2 to 6 carbon atoms, are dehydrogenated at temperaturesranging from about 800-1600 F., and controlling the dehydrogenatingconditions so that the predominant reaction is splitting ofi 2 atoms ofhydrogen from each hydrocarbon molecule to form the correspondingunsaturate. Steam may be added to the gases when using certaincatalysts. Then without cooling, the resulting products are utilized asthe heat carrier gas in the second or vapor-phase cracking stage. Ifnecessary, further heat can be added to or extracted from theseproducts, in any suitable manner, before they are admixed with the oilvapors in the cracking stage. The particular charging stock to becracked is first vaporized, and the resulting vapors separated from anyunvaporized material. The vapors are then further heated by indirectheat exchange, as in a pipe-still coil, to a predetermined temperaturewhich depends upon the ultimate degree of cracking desired. Thesuperheated vapors are then admixed with the dehydrogenation productsfrom the first stage and the mixture is discharged into an enlargedspace, or reaction chamber, of suitable diameter and length to providethe proper time interval required for the completion of the selecteddegree of conversion. As the conversion products leave the reactionchamber, they are cooled below the temperature at which furtherconversion would occur, by a spray of cool, previously formeddistillate. The reaction temperature and time interval selected for thecracking are those which cause a minimum of undesirable side-reactions,such as forming tar, free carbon. etc. But if any of these undesiredproducts are present in the reaction products, they are removed byscrubbing the cracked products with a heavy residuum. The crackedproducts are cooled, fractionated, and separated into recycle crackingstock, cracked motor fuel and fixed gases. These gases containingolefins from the first stage and fixed gases formed in the crackingstage are collected and passed at the necessary temperatures andpressures over suitable polymerizing catalysts; whereby, polymers,suitable for motor fuel, and having a high octane rating. are formed andby cooling and condensing are separated from any xed gases remainingunconverted. These final fixed gases are then separated into gaseshaving two or more carbon atoms and methane and hydrogen. The former arerecirculated through the dehydrogenating and subsequent stages of theprocess. The hydrogen and methane are partly or wholly vented from thesystem for such use as is deemed advisable,

It is apparent that, as thus described, the process is self-supportingin the sense that the fixed gases formed in the cracking zone make upthe feed stock to the polymerizing and dehydrogenation zones. As thusoperated, the final products of the process are cracked tars from thecracking zone, cracked motor fuel, polymer gasoline, and fixed gasescomposed principally of hydrogen and methane. By close control of thetemperaturetime relationship used in the cracking zone, the amount ofcracked tars formed will remain substantially constant over a ratherwide range of cracking temperatures used. But the relationship betweenthe volume of cracked gasoline and polymer gasoline is a function ofamount of. fixed gas formed in the cracking zone. If it is desired toincrease the yield of polymer gasoline, it is done by increasing theamount of i'lxed gases formed in the cracking zone at the expense of thecracked gasoline yield, by increasing the severity of the crackingconditions maintained in the cracking zone. Under these conditions thevolume of polymer gasoline is increased and the volume of crackedgasoline is decreased, but the latter has a higher octane rating, andsince polymer gasoline has a very high octane rating, the octane ratingof the combined polymer' and cracked gasolines can be very materiallyincreased at but little sacrifice in combined volumes.

When it is desired to increase the yield of polymer gasoline withoutdecreasing the yield of cracked gasoline, it can be done by augmentingthe volume of gases, recycled from the polymerization zone to thedehydrogenation zone, with suitable hydrocarbon gases from an outsidesource. 'I'hese gases preferably contain from 2 to 6 carbon atoms, suchas ethane, propane, the butanes, pentane, and hexanes, or even light.natural gasoline, either alone or in combination. And in passing throughthe dehydrogenation zone. these are dehydrogenated along with therecycled gases from the polymerization zone. As a result, the totalquantity of unsaturates produced, to be subsequently polymerized togasoline, is increased by an amount substantially equal to the quantityof gases added from the outside source. By this procedure. the yield ofpolymer gasoline can be varied between rather wide limits withoutmaterial change in the yields of cracked gasoline.

The two factors of primary importance in determining the yields percycle obtained in the cracking zone are the cracking temperatures andreaction time intervals used. Yields may be maintained constant eventhough the temperature-time conditions are varied. For instance, ifcracking temperatures are raised, the reaction time must be shortened,and if the reaction time is lengthened, the reaction temperature must belowered. Desired yields in the cracking zone are obtained, when addinghydrocarbon gases from outside sources, by suitable adjustments of thetemperature-time conditions used. Temperature conditions are varied byvarying the temperatures at which the dehydrogenated gases and oilvapors enter the cracking zone. Since the dehydrogenated gases and theoil vapors are separately heated, there is an almost unlimitedflexibility as to control of resulting temperature attained upon theiradmixture. The reaction time is controlled by the variation in volumesof the gases and oil vapors, at constant pressure, or by suitablepressure variations in the cracking zone, since all material passingtherethrough is in the vapor phase.

Separation of the cracking reaction products is obtained by conventionalmethods in conventional equipment as will be described elsewhere. Allcracked tars and free carbon formed in the cracking zone are separatedfrom the remaining reaction products in the scrubber and from thence arewithdrawn from the system. Insufciently cracked charging stock isseparated from the remainder of the reaction products in thefractionating equipment, and is Withdrawn therefrom and recycled throughthe cracking zone. Cracked motor fuel is separated from the fixed gasesin suitable condensing and separating devices, and is Withdrawntherefrom for such further treatment as is desired. The fixed gasesremaining are the feed stock for the subsequent polymerizing zone.- If avery low sulfur content oi' the polymerlzed motor fuel, as well ascracked motor fuel, is desired, the hydrogen sulfide contained in thexed gases is removed by any suitable methods and means before the gasesare passed through the polymerizing zone. If no hydrogenation of polymerproducts is desired in the polymerization zone, or if hydrogeninterferes with the action of the selected polymerization catalyst, it,too, may be separated from the hydrocarbon gases before the latter arepassed through the polymerization zone, by any suitable method andmeans. Although methane does not seriously interfere with thepolymerization of unsaturates, it is insensible to the usualdehydrogenating catalysts, used subsequent to the polymerizing zone, andunless it be needed as a heatcarrying agent in the cracking zone, may beeliminated from the system along with the hydrogen.

The remaining fixed gases are then passed through the polymerizationzone and over a suitable catalyst under such conditions of temperatureand pressure as are best suited to the particular catalyst used. Ireserve the right to the use of any suitable catalyst, but for the sake`of illustration will describe the use of one such catalyst. The gasesare compressed to 250-500 pounds per square inch pressure and passedthrough a heater in which they are heated to 350-500 F., and under thesepressures and temperatures are passed through catalyst cases filled withsolid phosphoric acid catalyst. In passing over the catalyst, theunsaturates are polymerized to compounds boiling within the motor fuelrange. If hydrogen and methane have been removed from the fixed gases,the products leaving the catalyst cases could be cooled to l65200 F. andpassed directly into a stabilizer where the polymers' suitable for motorfuel are separated from any remaining gases boiling below a selectedtemperature. Such gases will be largely ethane, propane, and thebutanes, or the corresponding olefins. These gases are part, at least,of the feed stock for the dehydrogenating zone. If hydrogen and methanehave not been removed from the fixed gases prior to polymerization, thepolymer products leaving the catalyst cases can be cooled and theliqueiiable'portion condensed and separated from the uncondensedportion. The condensed liquid can then be sent to a stabilizer where itis freed of undesirable light fractions such as propane and butane. 'Iheuncondensed portion is then sent through an absorption unit in which thehydrogen and part, or all, of the methane in the gas are separatedtherefrom and vented from the system. The remaining portion of the'gasthen serves as part, at least, of the feed stock to the dehydrogenatingzone.

The feed stock to the cracking zone may range from light naphthas, forreforming, to heavy residuums. All portions of the feed stocks which arevaporizable under operating conditions pass through the cracking zone..Suche portions as are not vaporizable are separated from the vaporizedportions and are withdrawn from the vaporizing stage. Heavy residuumsmay have their vaporlz-A able portions increased `by vis-breaking priorvto vaporization. By vis-breaking is meant mild cracking to gas oil inthe liquid phase. The fresh feed and recycle stock may be separatelyheated and vaporized, as when the fresh stock is a heavy a residuum; orthey may be combined, heated, and vaporized together as when gas oil isthe fresh charging stock. v y The accompanying diagrammatic drawingillustrates one specific form of apparatus embodying the features of thepresent invention and wherein the process of the invention may bepracticed. However, it is not intended tolimit the invention to thespecific form of apparatus illustrated.

Referring to the drawing, fresh charging stock for the system issupplied through line I and valve 2 to pump 3, which forces the freshcharge into line 5 and through heat exchanger 4, where it receives heatindirectly from the hot vapors leaving the scrubber. It next passesthrough valve B, which by judicious manipulation in conjunction withvalves 94 in a Dy-pass line and 98 in recycle stock line 92, regulatesthe distribution of fresh charging. stock and recycle stock betweenheating coils I and 93. When a heavy is'closed and valves B and 96 areopened so that the residuum is separately heated in coil I and therecycle stock in coil 93. When gas oil is the charging stock, valve 94is opened and valves 6 and 96 are manipulated so that the fresh chargingstock and recycle stock are distributed in proper proportions betweencoils 1 and 93. This distribution is further facilitated by by-pass 95and valves 91 and |60 in conjunction with valves 9 and 99. The chargingstock passing through line 5 enters heating coil 1, where it is heatedto above its vaporizing temperature at system pressure, and is thendischarged into line 9 and passes through valve 9 into evaporator I0.When a heavy residuum is the fresh charging stock, sufcient pressure ismaintained on coil I by valve 9 to enable the residuum to be v'lsbrokenin coil 1. In evaporator I0, the vapors are flashed from the heated oiland are separated from any unvaporized residue. The vapors leave theevaporator through valve II and pass through line I2 into thesuperheater coil I3 located in pipe-still |06, in which they are heatedto the desired temperature. They may even be partially cracked in thiscoil if ldesired. The superheated vapors leave coil I3 and enter line|05, passing therethrough into mixing chamber I4. The recycle stockpasses through valve 99 and line 92 into heating coil 93, where it isheated to a point above its vaporization temperature at system pressure,and is discharged through line 98 and valve 99 into evaporator |00,where vaporization occurs. 'Ihe vapors are separated from anyunvaporized residue and leave the evaporator through valve IOI, and passthrough line |02 into the superheating coil |04 located in pipe-still|06. In this coil they are heated to any desired temperature, even beingpartially cracked, if desired, and are discharged therefrom into line|05, and thence into mixing chamber |4. To keep heating coils I3 and |04in balance, vapors on the way to these coils through lines I2 and |02maybe distributed between the coils by means of by-pass valve |03.

TheA mixing chamber is any suitable device for thoroughly andsubstantially instantaneously admixing the superheated vapors with thedehydrogenated heat carrier gas. The purpose of `this'procedure is toinsure a thoroughly homogeneous mixture at uniform temperaturethroughout showing that perfect heat exchange by direct contact is hadbetween all parts of the heat carrier gas and the oil vapors. Thistransfer is accomplished by making the admixture take place practicallyinstantaneously so that no substantial amount of cracking can occur inthe mixable refractory shapes with which the chamber can be lined. Thepurpose of such lining is to enable variation of reaction times whilekeeping the pressure within the chamber at a preferred figure. Byprecisely controlling the temperature of the gas and oil vapor mixtureentering the residuum is the fresh charging stock, valve 94 76 reactionchamber and the time interval during 7 which the mixture remains in thechamber, such precise control of the cracking reaction is had, that Aofthe original volume of 30 API gas oil charging stock, I have recoveredin excess of '10% as cracked gasoline with a production of less than 4%as cracked tar.

The reaction products leave the reaction chamber through pipe I6 andenter scrubber I1. While passing through I6, or Just after entering I1,the temperature of the reaction products is lowered to a point at whichno further cracking will occur by the injection of light, previouslyformed distillate. This distillate is withdrawn from receiver 22 throughline I4, and is forced by pump ||2 into the stream of reaction products.'I'he amount of this cooling distillate injected or atomized into thereaction products is controlled by a thermostat control of the speed ofthe pump ||2. The thermocouple of the thermostat is placed in the streamof reaction products at a point subsequent to the introduction of thequenching liquid. When set at a desired temperature, the thermostatforces the pump to deliver only the amount of quenching liquid as willcool the reaction products to the desired temperature. While passingthrough the scrubber, the partly cooled reaction products are thoroughlyscrubbed with the heavy residuum oil withdrawn from the evaporators Iand |00 through valves |08 and ||0, then through line |03, and forced bypump through valve |54 into the scrubber. In case the residues from I0`and |00 are insuillcient in volume, a heavy residuum may be introducedinto the system through line |52 and valve |53 into line |09 for use inthe scrubber.

The fuel oil, or cracked tar. is withdrawn from the scrubber by pump I|3 which forces the oil into line ||5. The sensible heat in this oil maybe utilized to supply the heat requirements of the stabilizer column byclosing valve |25 and forcing the hot oil through valve |24 into theheating coil in the base of the column and out through valve |26 intoline |21 and thence to storage. If an excess of hot fuel oil isavailable, part of it maybe by-passed through valve |25 around theheating coil in the base of the stabilizer.

The partly cooled and thoroughly scrubbed reaction products vapors leavethe scrubber I1 through line |8, passing through heat exchanger 4, inwhich they give up part of their sensible heat to the fresh incomingcharging stock, and pass on into the fractionating column I9. In thiscolumn the hydrocarbons boiling above the boiling point range for motorfuels are fractionated out of the reaction products and are reiluxedback into the base of the column. 'Ihe hydrocarbons boiling within theboiling point range of motor fuel, and all fixed gases leave the top ofthe column through line 20, passing through condenser 2|, where thecracked motor fuel fraction is condensed, and into receiver 22. Thereflux medium/used for the fractionation in column I9 is part of thecracked motor fuel condensate which collects in receiver 22. It ispicked up by reux pump and forced through line ||1 onto one of the toptrays of column I8.

'I'he condensed motor fuel, collected in the bottom of receiver 22, iswithdrawn therefrom through a liquid-level controlled valve |55, passingthrough pump 8, which forces it through line valve IIS and valve |22into line |23 leading to cracked gasoline storage or such otherdestination as is desired. Ory if a stabilized product from the crackingunit is desired, valve |22 is closed, valve |20 opened and pump 8 forcesthe cracked motor fuel from receiver 22 through line |2| into astabilizer column |55, where all propane and lighter hydrocarbons areseparated from the motor fueland driven off, and only such butane isallowed to remain in the motor fuel as is necessary to cause a desiredReid vapor-pressure for the motor fuel, the excess butane being drivenon with the propane and lighter hydrocarbons. The stabilized motor fueldescends the stabilizer column |58 into the base thereof from which itis withdrawn through a liquid-level controlled valve |28 and cooler |29and line |30 to the stabilized motor fuel storage. The gases expelledfrom the stabilized motor fuel may be forced through valve |3|, valve|32 being closed, into line |34 and thence into line 1| containing heatcarrier gases, or it may be forced through valve |32, valve |3| beingclosed, into line |33 and thence into line 23 leading to the suctionside of compressor 25.

The fixed gases, separated from the cracked motor fuel in receiver 22,are withdrawn through line 23 and valve 24, by means of which thepressures in the cracking zone are regulated, and are drawn into thesuction side of compressor 25, which compresses them to the pressurerequired for subsequent treatments. The compressed gases leave thecompressor through line 25, passing through partial cooler 21, in whichthey are cooled to a temperature adequate to condense out the pentane orheavier fractions the gas may contain and enter receiver 28 where anycondensate formed in 21 is separated from the remaining fixed gases.'I'his condensate is withdrawn through the liquid-level controlled valve|40 by pump |4| and is forced through line |42 into line 50 and thenceinto the stabilizer column |55. The remaining fixed gases pass fromreceiver 28 through line 29 into scrubber 30, in which they arecontacted with a sulfurremoving agent which removes the hydrogen sulfidethe gases usually carry. Any suitable sulfur-removing agent may be used.By way of examples, such materials as Thylox, sodium carbonate, andcertain amine solutions or even water, under high pressures, aresuitable. These agents are introduced through line |39 and valve |38into the scrubber 30, passing downward countercurrent to the ascendinggases, and leave the scrubber through valve |33 and line |31. Thesesolutions may be regenerated in suitable equipment, not shown, andrecirculated through scrubber 30, if desired. The purified gases leavescrubber 30 through line 3| for the subsequent polymerizing treatment.

If a polymerizing catalyst is used whose action' is interfered with byhydrogen, the fixed gases pass through valve 32, valve 34 being closed,and line` 33 to equipment not shownfor separating the Cz and heavierhydrocarbons from the hydrogen and methane. The remaining hydrocarbongases are then passed back into the system through line 35 and valve 35into line 31.

If the hydrogen and methane have no effect on polymerization by theparticular catalyst used or if appreciable hydrogenation of the polymersis desired, as with mixed catalysts, the fixed gases pass through line3| and valve 34, valves 32 and 35 being closed, and line 31 into coil 33located in gas heater 39. 'I'he gases are heated in coil 38 to atemperature best suited for the particular catalyst used and passthrough line 40 and alterf nately through valves 4I and 42 into catalystchambers 43 and 44, and thence, through valves 45 and 46 into line 41,This arrangement is made so that catalyst chambers 43 and 44 can be usedalternately. That is, the catalyst in one chamber can be used forcatalyzing polymerization, while the catalyst in the other chamber isbeing revivifled. The polymerization products then pass through line 41into the condenser 48 where polymers, boiling within the motor fuelboiling point range, are condensed.

When hydrogen and methane are separated from the xed gas by passing thegas through line 33 to suitable separating equipment not shown, thepolymerization products leave condenser 48, passing through valve 49,valve being closed, and pass through line 50 into the stabilizer column|56, where the remaining xed gases are separated from the polymersboiling within the motor fuel boiling point range and pass through valve|3|, valve |32 being closed, into line |34 and thence into line 1|. Ifhydrogen and methane have not been previously separated from the xedgases, the polymerization products pass from the the condenser48'through valve 5|, Valve 49 being closed, into receiver 52 where theliquid polymers are separated from the remaining fixed gases. The liquidpolymers drain from receiver 52 through liquid-level controlled valve|44 and, if staiblization at this time is not desired, through valve|51, valve |46 being closed, into line |45 and thence to storage. Ifstabilization is desired at this time, the liquid polymer passes throughvalve |46, valve |51 being closed, through pump |43, thence into line 50and into the stabilizer column |56. The remaining xed gases leave thereceiver 52 through line 53 and valve 54 and enter absorber column 58,where the gases are scrubbed with a suitable menstruum which absorbs allC2 and heavier hydrocarbons. If the pressure of the fixed gases leavingreceiver 52 is insuicient to insure the absorption of all C2 and heavierhydrocarbons in the absorber column 58, then valve 54 is closed, valves55 and 56 are opened, and the gases are passed through compressor 51 inwhich they are compressed to a suitable pressure. The compressed gasesare then passed through a cooler, not shown, in which they are cooled toa suitable temperature for absorption, and are then discharged into line53, passing into absorber column 58. The cooler, notV shown, is ofconventional design andl may even be the evaporator of a ref-rigeratingmachine if very low 'temperatures are needed. for suitable absorption in58. The gases passing upward through the absorber column 58 arecountercurrently scrubbed with a suitable scrubbing menstruum whichabsorbs all C2 and heavier hydrocarbons. The remaining hydrogenandmethane leave the column through valve 59 and line |50,` passing tothe plant fuel line or such other destination as is desired. 'I'heabsorption menstruum, leaves the base of the column passingthroughlliquid-level controlled valve 6| into line 6.2,.thencefthroughheat exchanger 63 where it is heated up by indirect heat exchange withhot gas-free,- absorption menstruum from still 65 and enters still 65,In the still the gases are driven out-ofthe absorbing menstruum by heatsupplied throughasteam .coil 68,k and some open steam if desired, andleaves thestill through valve 10, entering line 1|. Any of the absorbingmenstruum vaporizedand carried by the gases ieaving the still arecondensed by reux condenser 69 and refluxed back downthe still column.The hot gas-free absorbing menstruum collects in the base of the stilland is withdrawn by pump 66,

10 forced into line 61, through heat exchanger 63, where it gives up aportion of its sensible heat to cold solution from absorber column 58,then passes through cooler 64 where it is cooled to the temperaturefound necessary for the most eicient separation of gases in column 68,and then enters the top of column 68. The cooler 64 may be theevaporator of a refrigerating machine, if low temperatures are foundnecessary.

The gasesl discharged through valve 10 and line |34 into line 1|,consist largely of hydrocarbons capable of being dehydrogenfated andsubsequently polymerized into compounds useful as motor fuel. From 1|they pass through valve 12 into line 18, and from thence into heatingcoil 19 located in pipe-still heater |06. If desired, steam may be addedto these gases, through line 16 and valve 15, or if their volume is tobe augmented by\hydrocarbon gases from outside sources, such gases maybe added through line 13 and valve 14. If thermal dehydrogenation onlyis to be used, valves |50 and |5| are closed and the gases are passedthrough valve |49 into superheating coil 88, thence into line 89, andare finally discharged into the mixing chamber |4. If catalyticdehydrogenation is to be used, valve |49 is closed and the gases passthrough valve |5| into' line 82, and then alternately through valves and8 I, dehydrogenating catalystchambers 83 and 84, valves and 86 into line81. Catalyst chambers 83 and 84 are used alternately so that thecatalyst in one may be used for dehydrogenating the hydrocarbon gases,while the catalyst in the other is being reviviiied. The dehydrogenatedgases pass from line 81 through valve |50 into superheating coil 88,`where they Aare heated to a predetermined temperature, and thencethrough line 89 into the mixing chamber I4.

As a speciflc example of one operation of the process of thepresentfinvention, the charging stock is a. 33` API ygas oil.y One partof fresh charging stock is mixed with two parts' of recycle stock andthe mixture is heated to approximately 850 F. Itis then flashedintovapors in the evaporators, and the vapors are then further heated in thesuperheater coils-to approximately 960 F. 'Ihesuperheated `vapors aremixed in a mixing chamber with the dehydrogenated` heat carrier gas atapproximately 1200 F. and of such volume that the resulting mixture hasa temperature of approximately 1010 F. The mixture discharges into thereaction chamber where it is held for 2 minutes, more or less, under apressure of approximately pounds per square inch gage pressure. vAs thereaction mixture leaves the reaction chamber, it is shock-chilledtoapproximately 800-880 F. by an Yinjection ofcold previously-formeddistillate, and enters the scrubber where any cracked tars and .freeAcarbon are scrubbed out of the` vapors. The vapors then pass throughaheat exchangerV where they heat up the incoming fresh charging stock to30W-400 F. and pass into the fractionating columnA where they areseparated into recycle stock and motor fuel plus xedfgases... Therecyclestocks `falls to the bottom of the column` and is Withdrawntherefrom `at approximately .500 F; i The vapors and fixed gases arewithdrawn from the'column at approximately 380 F. They are then cooledand their motor fuel content :condensed and sepparated from theuncondensed iixedfgases. 'Ihese latterf gases-are then .scrubbediwithfasodium carbonate solution to'4 remove their .hydrogen sulfide content,and then passed through absorption equipment which separates them into11 two fractions, one of which consists largely of hydrogen and methane,and the other consists largely of the C2 and heavier hydrocarbons. This'latter fraction is then compressed to approximately 500 pounds persquare inch gage pressure, heated to approximately 400 F., and underthis pressure and temperature is passed over a solid phosphoric acidcatalyst which polymerizes the unsaturates in the gas to a polymerliquid suitable for motor fuel. The products leaving the catalyst arecooled, the polymer liquid is condensed and separated from the remainingunconverted gases. These latter gases are heated to approximately 1200F., passed over an active alumina dehydrogenating catalyst, and at thistemperature enter the mixing chamber for admixture with the super-heatedoil vapors to be cracked. As thus operated, the yields obtained will beapproximately 10.8% fuel oil, 65.0% cracked gasoline, approximately 12%polymer liquid, and approximately 12.2% fixed gas. The ratio between theyield of cracked gasoline and polymers depends upon the amount of Czvandheavier hydrocarbons dehydrogenated and subsequently polymerized.Addition of such gases as propane from outside sources can increase verymaterially the yield of polymer liquid and fixed gases.

It is to be understood the reason for carrying out dehydrogenation,cracking, and polymerization in three separate zones or stages is thatoperating conditions and techniques may be employed in each of theseparate zones which are best suited to yield the maximum amount of theparticular products desired from the particular reactions occurring ineach of the separate zones, and yet the separate operations of the threeseparate zones are combined into a single, unitary process, asdescribed, by means of which the maximum possible yields of desiredproducts'are obtained with minimum yields of undesirable byproducts suchas cracked tars and fixed gases.

It is thought that the many advantages of the process in accordance withthis invention can be readily understood, and although the preferredembodiment thereof is as illustrated and described, yet it is to beunderstood that changes in detail of construction and operation can behad which fall within the scope of the invention hydrocarbons therein toolenes, thereafter heatlngthe gas to the cracking temperature and mixingit with the vaporized hydrocarbon charging stock, treating the crackedvapor-gas mixture to separate a cycle stock, a motor fuel distillate, agas residue and a liquid residuum, catalytically polymerizing gasresidue,separating polymer distillate from gas residue and returningg'as residue from which the polymer distillate has been sepa rated tothe dehydrogenation zone as heat car-y riergas.

2. The process dened in claim 1 in which the heat carrier gas iscatalytically,dehydrogenated and immediately superheat'ed before ',beingmixed with the vapors in the 'cracking zone.

vaporizing a hydrocarbon charging 3. The process defined in claim 1 inwhich the gases leaving the cracking zone are treated to remove hydrogenand methane before being introduced into the polymerization zone.

4. The process defined in-claim 1 in which the heat carrier gas istreated to remove sulfur constituents and catalyticallydehydrogenatedbefore being mixed with the vapors being cracked.

5. The process defined in claim 1 in which hydrocarbons containing C:and higher carbon atoms to the molecule are separated from thepolymerization residue gas and this separated gas returned to thedehydrogenation stage as a carrier gas.

6. The process defined in claim 1 in which the step of vapor phasecracking consists in vaporizlng the charging stock, separating theevolved vapors from the unvaporized residue, heating the vapors byindirect heat exchange, mixing the superheated vapors with the heatcarrier gas in a suitable device which thoroughly andsubstantiallyinstantaneously mixes the vapors and gas, and 'dischargingthe mixture of gas and vapors into an enlarged space of such diameterand length as to provide the necessary time interval for the completionof the desired degree of cracking while the mixture is travelingtherethrough.

'1. The process defined in claim 1 in which steam is added to thepolymerization residue gas before itis passed into thedehydrogenationzone.

8. The process defined in claim 1 in which the temperature inv thecracking zone is suillciently increased to increase the volume ofpolymer diso tillate while decreasing thel volume of distillate formedby cracking.

9.;The process defined in claim 1 in which gas from an external sourcecontaining C: and higher carbon atoms to the molecule is addedto thecarrier gas before introducing it into .the dehydrogenatlon zone, andsuperheating the dehydrogenated gas before passing it into the crackingzone to increase the volume of polymer distillate.

10. A vapor phase cracking. process comprising: vaporizing a hydrocarboncharge oil,4 separating residual oil from vaporized fractions,sup'erheating said vaporized fractionsadmixing heat carrier gas with thesuperheated vapors to raise the vapors to cracking temperature andpassing the mixture at cracking temperaturethrough a reaction zone,fractionating the reaction products to separate fractions heavier thangasoline, gasoline and gases. passing the gases to a catalyticpolymerization zone to polymerize olellnic coinponents .to gasoline,fractionating the polymerization products to separate out motor fuelfractions from unconverted residual gases, fractionating said residualgases to secure a fraction comprising principally C2 and heavierhydrocarbons, dehydrogenating said last mentioned fraction at elevatedtemperatures and withoutsubstantlal loss of heat, utilizing thedehydrogenated gases 'as the heat carrier gas irst' mentioned. l 11. Theprocess donned in claim v10 including the additional -step of promotingdehydrogenatioii 'of 'the heat carrier gas byl means of adehydrogenating catalyst. 'A

12. The process de ii'ned in claim 10 including the additional step ofadding to the 'unconvert'ed gaseous residue from the polymerizationzone, and prior to the dehydrogenase zone, an additional volume ofhydrocarbons, said hydrocarbons to contain from two to six carbon atoms.

13. The process deilined in claim 110 in which 13 the heat carrier gasis dehydrogenated and then superheated before being mixed with thesuperheated charging stock vapors.

14. The process defined in claim 1 in which the gases leaving thepolymerization zone are treated to remove hydrogen and methane beforebeing introduced into the dehydrogenation zone.

wrLLIAM 4o. KEELING.

REFERENCES CITED The following references are of record in the le ofthis patent:

Number UNITED STATESPATENTS Name Date Armstrong Jan. 4, 1927 BeardsleyJan. 19, 1932 Cooke Dec. 18, 1934 Sachs Sept. 6, 1938 Nelson Aug. 22,1939 Atwell Sept. 17, 1940 Thomas July 15, 1941 Boyd Aug. 26, 1941Borden Dec. 9, 1941 Seguy Mar. 10, 1942

